It is desirable when mooring objects in bodies of water for subsequent retrieval, such as subsea instruments mounted on a housing used for collecting and recording underwater data, to position the instruments below the surface of the water to obtain measurements at substantial depths, or alternatively to avoid damage or outright loss or dislocation due to wave action in storms or being struck by passing ships.
Underwater release mechanisms of which applicant is aware are shown in U.S. Pat. Nos. 3,848,226 and 4,136,415.
Retrieval of such moored instruments in the past has been accomplished by attaching a surface buoy attached with a cable to the instrument positioned to be picked up by a surface vessel, however such retrieval buoys run the same risks of outright loss and detection and are difficult to locate.
When deep water readings are desired, where instruments are anchored up to depths of 8000 meters, use of surface buoys has been found impracticable. Accoustical underwater release mechanisms have been developed such as disclosed in U.S. Pat. Nos. 3,848,226 and 4,136,415 where moored instruments have been provided which, at a remote command in the form of an acoustic signal, release the instruments from a mooring or apparatus or ground tackle, typically an anchor and cable, and permit the instruments attached to the release mechanisms typically connected to a flotation device to permit the instruments and release device to rise to the surface of the body of water to be retrieved upon sighting by a ship-borne retrieval party. Prior art acoustic underwater release mechanisms, particularly as referred to above, have employed a fixed post and movable-hook type release device for securing loads at substantial depths, wherein the acoustic release mechanisms having a top end and a bottom end are oriented in a upright position with the release mechanism attached to the bottom end and the mooring line and a floater buoy is attached to the top. Typically, explosive detonators are used to activate the release device to break open the release device to disconnect the moored object from the anchor and anchor cable. Such release mechanisms have provided adequate service at shallow depths, however at greater depths when the pressure is in the range of 10,000 PSI they have malfunctioned due to intermittent failure to overcome exterior water pressures and release the instrument from the mooring. Furthermore, such release mechanisms being unbalanced, when used at depths of 8000 meters where pressure of 10,000 PSI are encountered, tend to hang up as the release mechanism at times fails to overcome the substantial pressure acting against the single movable hook release device.